This is a short guide on how to install KDE 1 on Arch Linux.
Install qt1-git, kde1-kdelibs-git & kde1-kdebase-git from the AUR. Extra applications are avaiable in kde1-kdenetwork-git, kde1-kdetoys-git, kde1-kdegames-git and kde1-kdeutils-git.
You also have to have xorg-server & xorg-xinit installed. I have not tested KDE1 with a login manager (like sddm) so I can't help you with that.
Edit ~/.xinitrc and add the following lines
export PATH=/opt/kde1/bin:$PATH